2015-09-21T08:38:52ZRecent developments in Archeomagnetism: the story of the Earth's past magnetic fieldhttp://hdl.handle.net/2122/10165
Title: Recent developments in Archeomagnetism: the story of the Earth's past magnetic field
Authors: Pavón-Carrasco, F. J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Osete, M. L.; Univ. Complutense Madrid (Spain); Campuzano, S. A.; Univ. Complutense Madrid (Spain); McIntosh, G.; Canterbury Univ. (UK); Martín-Hernández, F.; Univ. Complutense Madrid (Spain)
Editors: Eppelbaum, L. V.; Telaviv Univ. (Israel)
Abstract: Since the pioneering studies in archeomagnetism in the second half of the 20th century, the number of archeomagnetic studies has increased exponentially. The huge density of archeomagnetic data collected during these years allows us to describe the past spatial and temporal evolution of the Earth’s magnetic field during the last millennia. Most of the data are located in the Northern Hemisphere, but currently, thanks to the strong effort of the paleomagnetic community, new collections of data are coming from the Southern Hemisphere, homogenizing the present database. Although the data distribution presents some epochs and locations where the data are still very scarce, they describe, to a greater or lesser degree of accuracy, the past behavior of the geomagnetic field. At regional scales, the use of archeomagnetic data permits the construction of paleosecular variation curves for the geomagnetic field elements: declination, inclination, and intensity. These curves describe the evolution of the elements at different times for the last millennia. During the last five years novel techniques, such as Bayesian statistics, bootstrap algorithms, or the Markov chain Monte Carlo method, have been applied to extract the most useful information from archeomagnetic data to build accurate and reliable curves. The accuracy of these curves can be exploited as a tool for archeomagnetic dating, assigning possible ages to archeological artifacts or volcanic lava flows with unknown age. At global scales, archeomagnetic data are jointly treated with other paleomagnetic data to generate continuous geomagnetic field models, reconstructing the past evolution of the geomagnetic field not only at the Earth’s surface, but also at the core-mantle boundary, shedding light on the past evolution of complex geodynamo processes.2015-08-31T22:00:00ZANNALS OF GEOPHYSICS: AD MAJORAhttp://hdl.handle.net/2122/9916
Title: ANNALS OF GEOPHYSICS: AD MAJORA
Authors: Florindo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bianco, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Muscari, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Caprara, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Chiodetti, A. G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Gresta, S.; Univ Catania
Abstract: Annals of Geophysics (ISSN: 1593-5213; from 2010, 2037-416X) is a bimonthly international journal, which publishes scientific papers in the field of geophysics sensu lato. It derives from Annali di Geofisica (ISSN: 0365-2556), which commenced publication in January 1948 as a quarterly periodical devoted to general geophysics, seismology, Earth magnetism, and atmospheric studies....2013-12-31T23:00:00ZNon-Dipole and Regional Effects on the Geomagnetic Dipole Moment Estimationhttp://hdl.handle.net/2122/9111
Title: Non-Dipole and Regional Effects on the Geomagnetic Dipole Moment Estimation
Authors: Campuzano, S. A.; Univ. Complutense Madrid, Spain; Pavón-Carrasco, F. J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Osete, M. L.; Univ. Complutense Madrid, Spain
Abstract: The study of the temporal evolution of the dipole
moment variations is a forefront research topic in Earth sciences. It
constrains geodynamo simulations and is used to correct cosmogenic
isotope production, which is evidence of past solar activity,
and it is used to study possible correlations between the geomagnetic
field and the climate. In this work, we have analysed the main
error sources in the geomagnetic dipole moment computation from
palaeomagnetic data: the influence of the non-dipole terms in the
average approach, the inhomogeneous distribution of the current
palaeomagnetic database, and the averaging procedure used to
obtain the evolution of the dipole moment. To evaluate and
quantify these effects, we have used synthetic data from a global
model based on instrumental and satellite data, the International
Geomagnetic Reference Field: 11th generation. Results indicate
that the non-dipole terms contribute on a global scale of <6% in
the averaged dipole moment, whereas the regional non-dipole
contribution can show deviations of up to 35 % in some regions
such as Oceania, and different temporal trends with respect to the
global dipole moment evolution in other ones, such as Europe and
Asia. A regional weighting scheme seems the best option to mitigate
these effects in the dipole moment average approach. But
when directional and intensity palaeomagnetic information is
available on a global scale, and in spite of the inhomogeneity of the
database, global modelling presents more reliable values of the
geomagnetic dipole moment.2014-12-31T23:00:00ZImproving total field geomagnetic secular variation modeling from a new set 3 of cross-over marine datahttp://hdl.handle.net/2122/8921
Title: Improving total field geomagnetic secular variation modeling from a new set 3 of cross-over marine data
Authors: Pavón-Carrasco, F. J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Torta, J. M.; Observatori de l'Ebre (Spain); Catalán, M.; Geophysical Dpt., Royal Spanish Naval Observatory (Spain); Talarn, A.; Observatori de l'Ebre; Ishihara, T.; Institute of Geology and Geoinformation, AIST (Japan)
Abstract: A new set of cross-over marine data has been used to generate a regional model for the secular variation of the total geomagnetic field, showing the potential of the suggested approach for gaining a better knowledge of the field over oceanic regions. The model, which is valid for the Northern Atlantic region during the temporal interval 1960–2000, was obtained using spherical cap harmonic analysis (SCHA) in space and penalized splines in time. The maximum spatial expansion is equivalent to degree 9 in ordinary spherical harmonic analysis. Annual mean intensity data from different geomagnetic observatories have been used to improve the spatial and temporal resolution of the original dataset. Results indicate that the regional model improves, in terms of the root mean square error, the prediction given by the 11th generation of IGRF and CM4 global models, especially for the geomagnetic observatories considered. We also provide the uncertainty of the model coefficients and the secular variation prediction given by a bootstrap algorithm. The model is available in the EarthRef. org Digital Archive at http://earthref.org/ERDA/1728/.2013-02-28T23:00:00ZA geomagnetic field model fo the Holocene based on archaeomagnetic and lava flow datahttp://hdl.handle.net/2122/8920
Title: A geomagnetic field model fo the Holocene based on archaeomagnetic and lava flow data
Authors: Pavón-Carrasco, F. J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Torta, J. M.; Observatori de l'Ebre (Spain); Osete, M. L.; Universidad Complutense Madrid (Spain); De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: We propose a new geomagnetic field model for the Holocene period based on archaeomagnetic and lava flow data, avoiding the use of lake sediment data. The source of data comes from the GEOMAGIA50v2 database which has been updated with the new archaeomagnetic and volcanic studies published during the last 3 years. The model, called SHA.DIF.14k, allows us to analyse the behaviour of the geomagnetic field for the last 14000 years: from 12000 BC to 1900 AD. For the model construction we use the spherical harmonic analysis in space and the penalized cubic B-splines in time. Both spatial and temporal regularization norms are used to constrain the inversion problem and applied at the core-mantle boundary (CMB) to assure the convergence of the model. For the last 3ka, the model predictions agree with those given by the global model ARCH3k.1 and the European model SCHA.DIF.3k. For older epochs, the new model presents a clear improvement in field resolution with respect to other current models of the geomagnetic field for the Holocene. For the last 9ka, the time evolution of the dipolar moment obtained from the dipole field shows a clear minimum between 5500 BC and 3000 BC, and the well-known continuous decreasing trend of the geomagnetic field strength for the last millennium and half. A general view of the time-average evolution of the geomagnetic field flux lobes at the CMB for the northern hemisphere suggests a marked lobe of positive magnetic flux when the dipole moment was maximum. This lobe vanishes when the dipolar field is decreasing. The north polar wander paths of both north magnetic dip and geomagnetic poles were obtained showing an average rate of motion of 5.1 km/yr and 3.7 km/yr respectively. The model shows that the geomagnetic field can be averaged as axial dipolar in ~2000 years within an error of 5º, the typical uncertainty of the palaeomagnetic studies. Finally, and following the recent definition of archaeomagnetic jerks, we found 8 critical events in the time-evolution of the geomagnetic field for the last 8ka characterized by a maximum in the hemispheric asymmetry of the proposed model. The model is available in the Earth Ref Digital Archive at http://earthref.org/ERDA/1897/.2014-01-31T23:00:00ZMonitoraggio sismico del territorio nazionale: stato dell'arte e sviluppo delle reti di monitoraggio sismicohttp://hdl.handle.net/2122/8813
Title: Monitoraggio sismico del territorio nazionale: stato dell'arte e sviluppo delle reti di monitoraggio sismico
Authors: Sergio, Guardato; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia
Abstract: Il sistema CUMAS (Cabled Underwater Module
for Acquisition of Seismological data) è un
prodotto tecnologico-scientifico complesso nato
con il Progetto V4 [Iannaccone et al., 2008] allo
scopo di monitorare l’area vulcanica dei Campi
Flegrei (fenomeno del bradisismo).
Si tratta di un modulo sottomarino cablato e
connesso a una boa galleggiante (meda elastica). Il
sistema è in grado di acquisire e trasmettere alla
sala di monitoraggio dell’OV, in continuo e in
tempo reale, sia i segnali sismologici sia quelli di
interesse geofisico ed oceanografico (maree,
correnti marine, segnali acustici subacquei,
parametri funzionali di varia natura).
Il sistema è in grado di ricevere comandi da remoto
per variare diversi parametri di acquisizione e di
monitorare un cospicuo numero di variabili di
funzionamento.
Il sistema si avvale del supporto di una boa
galleggiante attrezzata. La boa è installata a largo
del golfo di Pozzuoli (Napoli) a circa 3 km dalla
costa. Il modulo sottomarino, collegato via cavo
alla parte fuori acqua della boa, è installato sul
fondale marino a una profondità di circa 100 metri.2010-12-31T23:00:00ZRepeat-station surveys: implications from chaos and ergodicity of the recent geomagnetic fieldhttp://hdl.handle.net/2122/8683
Title: Repeat-station surveys: implications from chaos and ergodicity of the recent geomagnetic field
Authors: De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Qamili, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cianchini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: The present geomagnetic field is chaotic and ergodic: chaotic because it can no longer be predicted beyond around 6 years; and ergodic in the sense that time averages correspond to phase-space averages. These properties have already been deduced from complex analyses of observatory time series in
a reconstructed phase space [Barraclough and De Santis 1997] and from global predicted and definitive models of differences in the time domain [De Santis et al. 2011]. These results imply that there is a strong necessity to make repeat-station magnetic surveys more frequently than every 5 years. This, in turn, will also improve the geomagnetic field secular variation models. This report provides practical examples and case studies.2013-04-17T22:00:00ZCurie isotherm depth from aeromagnetic data constraining shallow heat source depths in the central Aeolian Ridge (Southern Tyrrhenian Sea, Italy)http://hdl.handle.net/2122/8669
Title: Curie isotherm depth from aeromagnetic data constraining shallow heat source depths in the central Aeolian Ridge (Southern Tyrrhenian Sea, Italy)
Authors: De Ritis, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Ravat, D.; Department of Earth and Environmental Sciences, University of Kentucky; Ventura, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Chiappini, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia
Abstract: The Salina, Lipari, and Vulcano volcanic ridge
and the surrounding sea sectors (Aeolian Archipelago,
Southern Tyrrhenian Sea, Italy) are characterized by vents
responsible for a recent (<40 ka—1889/1890 AD) effusive
and explosive subareal activity and repeated, 56 to 7 ka in
age, submarine explosive eruptions from source areas located
between Lipari and Vulcano. A spectral depth estimation of
the magnetic bottom using a fractal method on aeromagnetic
data from Vulcano, Lipari, and Salina volcanic ridge allows us
to constrain the Curie isotherm depth. The elevated portion of
the isotherm is between 2 and 3 km below Salina and Vulcano
and about 1 km below Lipari. The Curie depth results in the
context of other geological and geophysical evidence suggest
that the rise of the Curie isotherm is mainly due to the
occurrence of shallow heat sources such as magma ponds
and associated hydrothermal systems. The short-wavelength
magnetic anomaly field reflects magnetic contrasts from
highly magnetized volcanic bodies, low-magnetization
sediments, and hydrothermally altered rocks. Borehole temperature
data verify the Curie temperature derived from the
magnetic methods on the island of Vulcano.We conclude that
the whole Vulcano, Lipari, and Salina volcanic ridge is active
and should be monitored.2013-03-19T23:00:00ZAntarctic geomagnetic reference model updated to 2010 and provisionally to 2012http://hdl.handle.net/2122/8076
Title: Antarctic geomagnetic reference model updated to 2010 and provisionally to 2012
Authors: Tozzi, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Gaya-Piqué, L.-R.; On-Site Inspection Division, Comprehensive Nuclear-Test Ban Treaty Organization PrepCom, Vienna, Austria.
Abstract: The Antarctic Reference Model (ARM) has been here updated using recent geomagnetic data measured over the Antarctic continent from both ground observatories and satellites. This regional geomagnetic model is based on a Spherical Cap Harmonic Analysis (SCHA) of geomagnetic field measurements over a polar cap of 30° half-angle centred at the geographic South Pole, fixing the maximum spatial expansion index kmax=8 and the maximum temporal order of polynomials qmax=4.
The importance of updating ARM model lies, for instance, in its usefulness for the reduction of magnetic surveys, performed during the period of model validity over the Antarctica, or for geomagnetic anomaly field estimations. Moreover, so far, ARM still remains the only regional reference magnetic model specifically constructed for the Antarctic continent. The present updated version can be considered valid from 1955.5 to 2010.0 with predictive coefficients up to 2012.0. The model includes the most recent available data but, in contrast to previous versions not only does it take advantage of a stricter selection of satellite data in order to consider even quieter periods of external magnetic activity, but it also includes ground observatory data previous to 1960 going back to 1955.8. Like the previous versions, the new updated model has been tested and compared with major global models to show its reliability over the region under investigation.2012-12-31T23:00:00ZPaleomagnetic secular variation at the Azores during the last 3 kahttp://hdl.handle.net/2122/8009
Title: Paleomagnetic secular variation at the Azores during the last 3 ka
Authors: Di Chiara, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Speranza, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Porreca, M.; Centro de Vulcanologia e Avaliação de Riscos Geológicos, Universidade dos Açores, Ponta Delgada, Portugal.
Abstract: We report on 33 new paleomagnetic directions obtained from 16 lava flows emplaced in the last 3 ka on São Miguel, the largest island of the Azores. The data provide 27 well-dated
directions from historical or 14C dated flows which, together with 6 directions previously gathered from the same flows by Johnson et al. (1998), yield the first paleomagnetic directional record of the last 3 ka from the Atlantic Ocean. Within-flow directions are consistent, suggesting that inclination swings from 60 to 25 and declination changes between 10 to 20 reflect variations in the geomagnetic field over the last 3 ka. To a first approximation, the declination record is consistent with predictions from CALS3k.4 and gufm1 global field models. Conversely, inclination values are lower than model predictions at two different ages: 1) four sites from the 1652 AD flow yield I = 48 instead of I = 63
predicted by gufm1; 2) data from several flows nicely mimic the inclination minimum
of 800–1400 AD, but inclination values are lower by 10 than CALS3k.4 model predictions. By interpolating a cubic spline fit on declination / inclination versus age data,
we tentatively infer the directional evolution of the geomagnetic field at the Azores from 1000 BC to 1600 AD. The obtained curve shows three tracks in virtual overlap during the 1000–800 BC, 800–500 BC, and 400–700 AD time spans.2012-07-11T22:00:00Z